Luminous tube signage has been used for decades. Typically, a tortuous length of glass tubing is formed into the desired design. Next, electrodes are sealed to either end, with one electrode being tubulated. The tube is then processed: baked, exhausted, backfilled and sealed. A transformer then applies voltage across the electrodes and causes the gas to give off light.
The manufacture of the electrodes is time consuming and labor intensive. FIG. 1 shows a prior art arrangement for manufacturing such electrodes. Typically, an electrode shell 10 includes two conductors 12 attached thereto. The conductors are inserted into die block holes 14. A tungsten mandrel 15 is arranged beneath the tubulations and moves up into the tubulation as described below.
In operation, the entire arrangement of FIG. 1 is spun and heat is introduced in the area labeled 20 where the outer tube and inner tubulation overlap. Once outer tube 22 and inner tubulation 18 are red hot and plastic, the tungsten mandrel moves up inside the tubulation. Immediately thereafter, two press blocks (not shown for clarity) press area 20 inward, forming what is known in the industry as a pinch seal. The mandrel is then removed and the part annealed.
FIG. 1A shows the finished electrode. FIG. 1B is a side view of the finished electrode of FIG. 1A.
The problem lies in the fact that the parts must be loaded by hand. The process of inserting two wires attached to an electrode shell into two holes cannot be automated.
The prior art process for manufacturing electrodes is somewhat automated, but the machines must be manually loaded. Manual loading limits production drastically, and increases "shrinkage"; i.e. broken parts due to operator errors.
For example, the design of a neon electrode necessitates manual loading by an operator. On an 8 head machine, an operator must perform a lengthy sequence of steps including (i) load a tubulation, (ii) insert an electrode shell with its two conductors engaged into two 0.030 diameter holes (iii) load an outer tube, and (iv) remove one finished part. This sequence is typically performed every 12 seconds, constantly, all day. The process produces approximately 300 electrodes per hour, less shrinkage of about 5% for a good operator.
Consider a glass part designed to be mass produced, such as a glass stem for a florescent lamp or a light bulb. These parts are produced without labor on a machine producing approximately 4000 per hour with about 2% shrinkage.
In view of the above, it can be appreciated that there exists a need for an improved design and manufacturing process for luminous tube electrodes which allows full automation and mass production.